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    <title>Document</title>
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    <script>
        // 遍历所有的字符
        let str = '你是否在云上';
        // 1. 索引号
        for (let i = 0; i < str.length; i++) {
            console.log(str.charAt(i));
        }

        // 2. for —— in
        for (let i in str) {
            console.log(i, str[i]);
        }

        // 3. for —— of
        for (let i of str) {
            console.log(i);
        }
    </script>
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